Photoresponsive Molecular Crystals for Light-Driven Photoactuators

Abstract

Various types of photomechanical motion have drawn much attention because there is a potential to create photomechanical actuators from molecularscale to macro-scale. To construct photoactuators, it is necessary to utilize a molecular assembly with a small free volume. Photochromic compounds undergo photoreversible isomerization between the original colorless isomer and the photogenerated colored isomer upon alternating irradiation with UV and visible light. Among many known photochromic compounds, diarylethenes undergo photochromic reactions even in the crystalline phase. The present review introduces recent development in the study of photomechanical crystals including crystal shape changes, bending velocity, dependence of the bending behavior on irradiation wavelength, the behavior in mixed crystal, new types of photomechanical motion, and applications. These photomechanical behaviors are based on geometrical structure changes in the crystalline phase and can be applied to macro-sized light-driven photoactuators.